Concrete blocks are used to form free standing and retaining walls. In such applications, the visible face or faces of the blocks are often provided with a textured or decorative appearance. Concrete blocks for forming walls are used in a variety of applications from small gardening applications to large-scale construction projects. Blocks are stacked in horizontal rows called courses. Multiple successive courses may be used to create a vertically rising wall of a desired height.
The concrete blocks used in constructing such walls are often manufactured using the dry cast process, which uses dry-cast block machinery to form blocks at a relatively high rate of speed. In a typical dry-cast block machine, material is fed into an open top mold from the top side. The conventional mold consists of stationary sides, to define the sidewalls of the block, and an open bottom. A removable pallet is used to temporarily close the open bottom of the mold and serve as a base during the block forming operation.
During manufacture, the material introduced through the open top collects on top of the pallet and is bounded by the end and side panels. A compression head is then pressed downwards under high pressure onto the material through the open top of the mold to compact the material therein. The head forces material into the mold so as to conform to the shape of the mold. The mold may also be vibrated during compaction to promote uniform compaction. The head may also be provided with one or more shoes that have relief defined therein in order to impart detail into the material that is contacted by the head's movement.
After compaction and vibration, the bottom pallet drops down, the head follows the pallet and the newly made product downward while the sides of the mold remain in position, and when the product clears the bottom of the mold, the pallet moves away from the mold and another pallet moves in place to make the next product. The head returns to its original position and the feed drawer brings more material into the mold to make the next product. The molding machinery is able to cycle several times per minute.
U.S. Pat. No. 5,827,015 teaches the use of conventional dry cast molding methods to form a twinned concrete slug in the molding machinery. The slug is then split into two blocks after being cured. It should be appreciated that the top surface of the finished wall block made according to the conventional dry cast manufacturing method is formed by the surface of the steel pallet. The bottom of the block is accordingly formed by the stripper shoe.
The need to eject the formed blocks through the bottom of the mold used in dry cast manufacture places limitations on the ability to create a decorative front face on the block because the sidewalls of the mold shear across the side surfaces of the block when stripped from the mold. Therefore, efforts have been made to provide for a decorative front face on concrete wall blocks.
One common current method of producing a wall block with a decorative front surface is to split a cured block (or a twinned slug) so that the front surface of the block has a fractured concrete surface that looks somewhat like split rock. This is done by forming a slug in a mold and providing one or more grooves in the slug to function as one or more splitting planes. The slug is then split apart to form two or more blocks. The appearance of the face of such block is exhibited by U.S. Pat. No. D380,560. This gives the front face of structures built with these blocks some visual depth that makes the structure look more natural. The number of facets and their arrangement can be varied to provide for different looks such as shown in U.S. Pat. No. D429,006.
More recent references, such as U.S. Pat. No. 6,321,740, disclose modification of the splitter blade used in splitting the cured block to provide edges that appear more weathered. Splitting, however, adds additional production costs by requiring an additional step to the manufacturing process and results in waste material. Furthermore, split-faced concrete blocks do not sufficiently resemble natural stone to satisfy some consumer needs.
Another method to make blocks that have decorative front surfaces is described in U.S. Pat. Nos. 5,078,940; 5,217,630; and 6,224,815. These patents describe a method and an apparatus for manufacturing a concrete block having an irregular surface. The irregular surface can be made to look similar to split stone. This method includes pouring uncured block material into a mold cavity and causing a portion of the material to be retained in place relative to the cavity walls when the block is removed from the cavity. The result is a somewhat split appearance for the surface, without having to perform the splitting operation. However, the block produced from this method still does not satisfactorily resemble natural stone.
Other methods employed to provide for improved decorative appearance include spraying the front face of an uncured block to wash away some cement to leave exposed aggregate. Another method consists of “weathering” a cured block by tumbling it in a tumbler with tumbler chips that knock off random pieces of the block, which rounds the ends and creates a look closer to the appearance of weathered stone. These methods, however, are labor intensive and can damage the blocks, resulting in a higher overall cost of production.
Commonly owned, copending application Pub. No. US 2004/0218985, which is hereby incorporated by reference in its entirety, discloses an alternative method of providing a decorative simulated natural stone face to the front surface of a block while using the dry cast manufacturing method. The molding apparatus is configured such that the front surface of the block faces up in the mold and can therefore be provided with a pre-defined decorative face because the shoe stamps or contacts it directly. This process, however, limits the ability to provide for sidewalls that deviate from conformance to the smooth vertical sidewalls of the mold box because the downward movement of the block through the mold prevents a mold with stationary angled sidewalls or relief from being used.
U.S. Patent Pub. Nos. 2003/0126821 and 2003/0182011 disclose a block machine that stamps a face on the front surface of a block while also providing a tapered sidewall to the block by use of pivoting sidewalls. However, this system does not teach the ability to impart a complex decorative face on the side surfaces of the blocks. In addition, the mold must be taken apart to a degree that makes it difficult to perform maintenance or repairs of the biasing mechanisms. This difficulty can cause undesirable delays in production.
A block and a method of making a block having two or more adjacent decorative faces is disclosed in commonly owned, copending U.S. Patent Publication No. 2007/0193181. The method involves utilizing a core puller mechanism to move end liners to a first, or fill, position to impart one or more decorative side faces as the block is formed. Before the block is stripped from the mold, the core puller mechanism pulls the end liners back to a second, or strip, position so that the decorative side faces are not damaged as the block is released. A drawback, however, is that the core puller mechanism is a large and complex piece of machinery that requires a large amount of space on the production floor and can take a significant amount of time to setup and install. Additionally, the moving parts in the mold may sometimes lack sufficient stability during various stages of molding, thereby causing undesired cracking of the block.
What is still needed in the industry is a system and method of making a block having two or more adjacent decorative faces that may more closely resemble natural stone or other decorative masonry element.